This invention relates to a method of manufacturing a composite refractory article having a flow passage through which a molten metal stream may be conducted and comprising a first body of refractory material which defines a surface of that passage, such first body being bonded to a second body of refractory material. The invention also includes composite refractory articles of the type referred to.
The composite refractory articles with which this invention is particularly concerned are useful as parts of and fittings for apparatus used in metallurgy and more particularly in foundry practice. Such articles include pieces used to guide or control the flow of molten metal streams such as slide plates and collector nozzles of sliding gate valves.
A problem encountered in foundry practice is the erosion of refractory material by a molten metal stream which flows past it. For example it is known to use a magnesia-based sliding gate valve plate for controlling the flow of molten steel from a pot furnace, but generally speaking the valve plate requires replacement each time the pot furnace is filled because the flow of steel through the flow passage in the slide plate tends to enlarge that passage and make it irregular. After use such valve plates are discarded. It is also known to make such vulnerable refractory parts of a higher grade of refractory material such as alumina, but this is expensive. It is also known to cement inserts of high grade refractory material, for example zirconia, into bodies of refractory material at their most vulnerable regions. This is inconvenient in practice since the insert and the remainder of the refractory body must be carefully matched in shape and size.
Furthermore, it is known from Flogates Limited's British Patent Application No. GB 2 065 278 A to form a refractory article having a surface portion which, in service, is contacted by a molten metal stream, comprising an integral composite body having a first refractory member providing the surface portion, a trough or cup shaped metal foil encompassing the first refractory member, and a second, back-up refractory member supporting the foil-encompassed first refractory member, the first refractory member being made from a higher duty refractory material than the second refractory member. This Flogates application also teaches a method of making such a refractory article including the steps of (i) forming a first mould space from a trough or cup shaped metal foil and a companion, permanent mould member the shape of which is a negative of the surface portion; (ii) filling the first mould space with a mouldable refractory concrete and at least partially curing the concrete; (iii) assembling the foil and moulding therein a second mould space formed from companion mould members; (iv) filling the second mould space with a second refractory concrete which is of lower duty than the first concrete; and (v) curing the second concrete and, to the extent that it may not already be completely cured, the first concrete also.